Method of tube bending



June 20, 1961 o. w. HEIMBERGER METHOD oF TUBE BENDING 4 Sheets-Sheet 1 Filed April 24, 1957 INVENTOR.

ATTORNEYS ScrWHezmbelger BY INYENTOR. scwz' Wflemabezger BY 4 Sheets-Sheet 2 ATTRNEYS O. W. HEIMBERGER METHOD OF TUBE BENDING June 20, 1961 Filed April 24, 1957 June 20, 1961 o. w. HEIMBERGER 2,989,109

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W y@ M S t?! scwrWHez/mberger BY F095 Fb'g gw@ AT TRNEKS 4 Sh cs-Sheet 4 Filed April 24, 1957 N wr V v Q N d mw mm IININIIINW l, In wulnnwmwiuiuhwhl J wijd Fw/ /T gauw/ AT TRNEYS' United States Patent C) 2,989,109 METHOD F TUBE BENDING Oscar W. Heimberger, Massillon, Ohio, assignor to The Griscom-Russell Company, Massillon, Ohio, a corporation of Delaware Filed Apr. 24, 1957, Ser. No. 654,786 1 Claim. (Cl. 15S-'40) This invention relates to a method for bending tubular products and it particularly pertains to apparatus for bending tubes and pipes.

Methods and apparatus for bending tubular products have been in use for many years. Generally where the resulting bend has a radius of at least two to three times the diameter of the tube there is no particular problem involved. Where the tube, however, is bent to ja radius equal to one or one and a half times the tube diameter, a problem of the distortion of the tube wall becomes critical. The distortion problem has two facets; namely, the elongation and thinning of the tube wall at the outer radius of the bend and the buckling or warping of the tube at the inner radius of the bend.

Where tubes having relatively thick walls are involved, the problem of thinning of the tube wall at the outer bend radius during the bending operation is less significant, so long as the nal wall thickness is sufficient to withstand whatever pressures the tube may be subjected to. However, Where thin-wall U-tubes are contemplated for use under high pressures such as in heat exchangers, the problem of the thinning of the tube wall at the outer radius of the U-bend is of utmost importance.

Associated with the problem of thinning of the tube wall portion at the outer radius of the bend is the problem of maintaining the original circular internal cross section of the tube due to the combined effect of high tensile stresses created during bending as well as to the lack of suicient support is adjacent portions of the tube wall to support the outer portion during the bending operation.

Recent tendencies in heat exchanger practice have involved the use of thin-wall tubes having U-bends, the radii of which are one to two times the tube diameter. By using thin-wall tubes a more efficient heat exchange can occur between the heat exchange lluids moving through the heat exchanger at high pressures. Accordingly, during the bending operation the tube must be neither thinned at the outside radius of the bend nor warped or buckled at the inside radius to withstand the high pressures.

It has been found that thin-walled tubes for use in high pressure heat exchangers may be provided with U-bends having radii ranging from one to two times the diameter of the tube. By performing the bending operation so that the outer circumference of the resulting bent portion is equal to the length of the straight tube before bending, the portion of the tube at the outer circumference is not subjected to tensile stresses which cause permanent -elongation and thinning of the tube wall. This method of bending may be performed with or without a mandrel.

Accordingly, it is a general object of the present invention to provide a new method and apparatus for the manufacture of U-tubes which avoid the diculties, disadvantages and limitations of prior methods and apparatus.

More specifically, it is an object of the present invention to provide a method of, and apparatus for, the manufacture of U-tubes for heat exchangers by which the outer bent portion of the wall of the tube is neither elongated nor thinned during the bending operation.

It is another object of the present invention to provide for the manufacture of U-tubes for heat exchangers, the

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inner portion of the U-bend of which is devoid of distorted tube wall and has a circular internal cross section.

It is another object of the present invention to provide a method for the manufacture of U-tubes, the circumference of the outer bend radius of which is equal to the length of the original straight tube segment forming the U-bend.

It is another object of the present invention to provide apparatus for the manufacture of U-tubes which provides an undistorted U-bent tube from an original straight tube.

Finally, it is an object of the present invention to provide an improved method of, and apparatus for, the manufauture of U-tubes which accomplish the foregoing desiderata in an inexpensive manner and with simplied tool design adjustment, maintenance and oper-ation.

'Dhese and other objects and advantages apparent to those skilled in the art from the following description and claims may be obtained, the stated results achieved, and the described difficulties overcome, by the methods, steps, procedures, operations, apparatus, parts, elements and combinations which comprise the present invention, the nature of which is set forth in the following general statements, a preferred embodiment of which--illustrative of the best mode in which applicant has contemplated applying the principles-is set forth in the following description and shown in the drawings, and which are particularly and distinctly pointed out and set forth in the appended claims forming part hereof.

The nature of the improved method of manufacturing U-tubes of the present invention may be stated in general terms as including the steps of placing a str-aight portion of tube to be bent between two aligned clamps, and moving one clamp through a cycloidal path from the aligned position to a position parallel to the other clamp, the circumference of the outer portion of the resulting U-bent tube being equal to the length of the original straight tube.

The nature of the improved apparatus of the present invention may be stated in general terms as including a base plate having an elongated slot therein, `a first clamp xedly mounted on the base plate and aligned with the axis of the slot, a second clamp movably mounted on the base plate and movable between `a position aligned with the rst clamp and a position parallel to the iirst clamp, the second clamp including a shaft portion located in the slot and movable therealong, the shaft portion having a pinion gear thereon, a driven rack engageable with the pinion gear and reversely movable in two directions for rotatably moving the shaft portion of the clamp along the slot between said positions of the clamp, a second rack mounted on the plate and engageable with the pinion gear, and a plurality of tube-supporting U-shaped members mounted between the clamps in the aligned position and so constructed as to snugly engage the outer semicircular portion of the tube during the movement of the second clamp from the aligned to the parallel positions with respect to the first clamp.

By way of example, a preferred embodiment of the method and apparatus of the present invention is shown in the accompanying drawings, wherein:

FIG. 1 is a plan view of the apparatus showing a straight tube mounted between the aligned clamps;

FIG. 2 is a plan view showing the alternative position after the bending operating;

FIG. 3 is an end view of the apparatus as shown in FIG. l;

FIG. 4 is a diagrammatic plan view showing the cycloidal path through which the movable clamp moves during the bending operation;

FIG. 5 is a vertical sectional view taken on the line 5-5 of FIG. 1;

FIG. 6 is a vertical end view taken on the line 6-6 of FIG. l;

FIG. 7 is a side elevational view of the apparatus as viewed in FIG. 1; and

FIG. 8 is a vertical sectional Iview taken on the line 8-8 of FIG. 7.

Similar numerals refer to similar parts throughout the various figures of the drawings.

In FIG. 1 a tube 1 is mounted in an apparatus for bending tubular products generally indicated at 2. The apparatus includes a base plate 3 having `an elongated slot 4 therein, a stationary clamp 5, a movable bending die 6, a movable clamp 7 attached to the bending die, and means for moving the die including a rack 8. In addition, the means -for moving the die 6 includes a fixed rack 9, a gear 10 attached to the die 6, a worm 11, a worm gear 12, a drive gear 13 and an idler gear 14.

Moreover, the apparatus 2 is provided with means for reinforcing t-he tube 1, which means includes a plurality of tube-engaging members 15 and a backup bar 16 for the members. Finally, the apparatus 2 is provided with an elongated mandrel 17 that is connected to a retraction bar 18 by a connecting link 19.

The stationary clamp is mounted on the base plate 3 by similar screws 20 (FIG. 6). 'Ihe clamp 5 includes a jaw 21 and both are provided with arced grooves 22 and 23, respectively, for gripping the outer surface of the tube 1 when the jaw 21 is tightened on the tube 1 by screws 24.

Likewise, the clamp 7 which is an integral part of the bending die 6 is provided with a clamping jaw 25 and the oppositely facing surfaces of the clamp 7 and jaw 25 are provided with arced grooves 26 and 27 yfor gripping the outer surface of the tube 1 when screws 28 are tightened.

As shown more particularly in FIGS. 3 and 8, the bending die 6 is semicircular in shape and includesv a tubereceiving groove 29 that is aligned with the groove 26 on the clamp 7, whereby upon rotation of the die 6 about its center in a manner shown in FIG. 4, the tube 1 occupies the groove 29.

The bending die 6 is mounted on a pin 30 to which the die is keyed. In addition, the gear is mounted on the pin 30 to which it is also keyed. The lower portion of the pin 30 extends through the slot 4 in :a slip fit manner. Moreover, the retraction bar 18 is apertured at 31 and the pin 30 extends therethrough (FIGS. 1 and 3). A washer 32 is disposed between the base plate 3 and the bar 18 and a retaining nut 33 engages the lower threaded end portion 34 of the pin.

The fixed rack 9 is mounted on the upper surface of the base plate 3 where it is retained by spaced screws 35 and the rack is engaged by the gear 10 as it moves from the position of FIG. l to that of FIG. 2. The movable rack 8 is parallel to the fixed rack 9 and engages the opposite side of the gear 10. The rack 8 includes gear surfaces on opposite sides so that the side opposite the gear 10 is engaged by the drive gear 13 and the idler gear 14. Both gears 13 and 14 function to maintain the rack 18 parallel to the rack 9 and in engagement with the gear 10 during the longitudinal movement of the rack 8.

The drive gear 13 is keyed to a pin 36 which extends through the base plate 3 and on the lower end of which is keyed the worm gear 12. The worm 11 is keyed to a worm shaft 39 the ends of which are mounted in journals 37 and 38 attached to the undersurface of the plate 3 (FIG. 1) and the outer extremity of the worm shaft 39 has a square cross section 40 to receive a hand crank (not shown).

Accordingly, by rotating the worm 11 the rack 8 is moved to the right as viewed in FIG. l, which motion is transmitted to the bending die 6 and clamp 7 through the gear 10 and the pin 30. Rotation of the gear 10 causes it to travel along the fixed rack 9 whereby the pin 30 moves along a slot 4 to the position shown in FIG. 2. By this operation the pin 30 travels in a straight line along the 4 slot 4 and the end of the tube 1 travels through a cycloidal path 41 (FIG. 4). The outer circumference of the resulting bent tube is equal to the length of the originai tube before bending; thus, no elongation, stretching or thinning of the outer portion of the tube wall occurs although the wall portion of the tube forming the inner part may be thickened due to compressive forces created A in the tube during the bending operation.

- werge-shaped portions a are closed when the wedgeshaped portions are brought into contact with each other until the tube 1 is completely bent around the semicircular bending die 6.

The members 15 reinforce the entire outer wall of the tube 1 from the upper to the lower sides thereof and thereby prevent any tube wall portion from expanding out wardly and thereby preventing another adjacent portion from collapsing. Thus, the original circular opening of the tube 1 is retained throughout the bending operation.

As shown in lFIGS. 1 and 5, the members 15 are retained in place by means of a pair of spaced flexible members 43 and 44 which extend between and are attaohed to similar plugs 45 partially seated within a portion of the clamp 7 at one end, and at the other end are secured to similar tightening screws 46 in the clamp 5. The flexible members 43 `and y44 extend through spaced grooves 47 and 48 in the upper and lower portions of the members 15. The exible members 43 and 44 are retained in the grooves by similar blocks 49 and 50 fitting into corresponding recesses in the members 15 and retained therein by screws 51. The grooves 47 and 48 in all of the members 15 are aligned with each other and with openings in the clamps 5 and 7.

The backup bar 16 for the members 15 is secured to the base plate 3 by screws 52 and the bar retains the members 15 in alignment both before and during the bending operation. The tube 1 may exert radial forces upon the members 15 still in contact with the bar 16, which forces would cause said members to move out of their positions of alignment with each other were it not for said bar.

During the bending operation a tube 1 composed'of one type of metal may or may not require the use of the mandrel 17. As best shown in FIGS. 4 and 8, the mandrel 17 is an elongated rigid member having an arcuate inner end surface 53, the radius of which surface corresponds to the radius of curvature of the resulting U-tube. Thus, the end surface 53 of the mandrel 17 is held in contact with the inner surface of the tube at the point of bending thereof. As the bending operation proceeds, the mandrel 17 is retracted by the retraction bar 18 which moves to the right, as shown in FIG. 8, with the bending die 6.

Accordingly, the apparatus 2 provides a device for bending tubular products without distortion of the tube. The apparatus 2 is designed to bend the tube by maintaining a circumference at the outer portion of the resulting bend equal to the length of the segment of tube forming such bend. The outer portion of the tube 1 is neither elongated nor stretched from its original length, for which reason the wall forming the tube is not thinned or reduced to any substantial degree. On the other hand, the portion of the tube forming the inner wall of the bend is thickened because the bending operation is preferably carried out at a rate slow enough to permit the metal forming the inner wall of the bend to flow without11 buckling or forming other distortions in the tube wa Referring particularly to FIGS. 1, 2, 4 and 8, the apparatus is constructed, as previously described, so that the outer circumference of the bend of the resulting bent tube is equal to the length of the original tube before bending in order that no elongation, stretching or thinning of the outer portion of the tube wall occurs. This is accomplished not only by holding the distance lbetween the left end of stationary clamp S (FIG. 1) and the right end of movable clamp 7 constant throughout the bending operation by the flexible cable members 43 and 44 which hold the tube-engaging members 15 in engagement with the tube 1; but also by locating a plane tangent to the outer circumference of the tube 1 and normal to the base plate 3, indicated by the line 54 in FIG. l, to pass through the pitch line of the gear teeth of the stationary rack 9.

Thus, there can be no stretching of the metal in the outer portion of the tube wall because, as the tube is -bent by movement of the bending die 6 from the position of FIG. 1 to the position of FIG. 2, also indicated by the dot-dash and full line positions of the parts illustrated n FIG. 4, along with the gear which is fixed relative to die 6, the metal in the outer portion of the tube wall as the tube is bent, is located parallel with the pitch line of the teeth of the gear 10, which teeth are engaged by and controlled by the teeth of the stationary rack 9.

Accordingly, one of the critical aspects of the present invention is the maintenance during bending of a fixed length for the portion of the tube being bent coordinated with the location of the tube metal at the outer bend circumference to be parallel with the pitch line of the rack 9 prior to bending and with the pitch line of the gear 10 during bending.

The structural arrangement and coordination of the parts as described, produces movement of a point indicated at P in the drawings, in the cycloidal path 41 illustrated in FIG. 4, during bending. The point P is located at the upper surface of the groove 27 of the clamping jew 25 which cooperates with movable clamp 7 at the extreme right end of movable clamp 7; and the point P coincides with a point at the initial zone of tu-be bending located at the top surface of the tube and which lies in the outer circumference of the resulting bend.

The half-round shape of the grooves in the tubeengaging members 15, which engage the upper semicircular segment of the outer circumference of the tube wall during bending, maintains the tube wall truly circular in cross section, and prevents any out-of-round formation of the tube wall from occuring during bending.

As indicated in FIGS. 4 and 8, the mandrel 17 retracts to the right as the movable die 6 moves to the right so that the arcuate inner end surface 53 of the mandrel en- "gages the inner surface of the tu'be wall at the point of bending at all times during bending. This is accomplished by the connection between the retraction bar 18 which controls movement of the mandrel 17, with the pin shaft 30 of the movable die 6 so that the retraction bar 18 moves to the right at the same rate that the movable die 6 moves to the right along slot 4 parallel with the position of the aligned clamps 5 and 7 in FIG. 1.

The movement of the movable clamp has been illustrated and described as occurring from an aligned position of the movable and stationary clamps to a position in which the clamps are parallel, as illustrated in FIG. 2, in order to produce a bend. However, it is not necessary, for the purposes of the present invention, that the nal position of the clamps be parallel, as any desired degree of bend less than or greater than 180 can be made depending upon the distance that the movable die 6 travels along the Ab-ase plate slot 4 from the starting position illustrated in FIG. 1.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art; because such Words are used for descriptive purposes herein and not for the purpose of limitation and are intended to be broadly construed.

Moreover, the invention is not limited to the exact apparatus shown because the particular arrangement of the parts may be varied to provide other structural embodiments without departing from the scope of the present invention.

Having now described the features of the invention, the construction and operation of a preferred embodiment of improved apparatus, the details of the steps of the improved method, and the advantageous, new and useful results obtained thereby, the new and useful inventions, methods, steps, procedures, operations, apparatus, parts, elements and combinations, discoveries, principles, and reasonable mechanical equivalents thereof, obvious to those skilled in the art, are set forth in the appended claim.

I claim:

In a method of forming a lbend in a tube intermediate the ends of a tube which includes the steps of circumferentially holding a first portion of the tube stationary, circumferentially gripping a second portion of the tube at a location spaced longitudinally from said rst portion, forming a bend in the tube between said first stationarily held portion and said second gripped portion by moving in a cycloidal path a point in the outer surface of the tube located at a position of maximum radius of the bend being formed and located within the space between said first stationarily held and second gripped tube portions, and holding said point at a constant peripheral distance from said rst stationarily held tube portion throughout its cycloidal path movement; whereby the bend is formed without elongating or stretching the tube wall at the maximum radius of the formed bend, thereby preventing thinning of the bent portion of the tube wall.

References Cited in the tile of this patent UNITED STATES PATENTS 784,101 Brinkman Mar. 7, 1905 1,268,844 Holinger June 11, 19'18 1,754,635 McCarthy Apr. 15, 1930 1,847,200 Vollmerhaus Mar. 1, 1932 1,877,629 Replogle Sept. 13, 1932 2,316,049 Connor Apr. 6, 1943 2,536,738 Green Ian. 2, 1951 2,743,756 Fredericks May 1, 1956 FOREIGN PATENTS 456,403 Great Britain Nov. 9, 1936 

